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Commit cbb38e41 authored by Dan Williams's avatar Dan Williams Committed by Linus Torvalds
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dax: provide diagnostics for pmd mapping failures 



There is a wide gamut of conditions that can trigger the dax pmd path to
fallback to pte mappings.  Ideally we'd have a syscall interface to
determine mapping characteristics after the fact.  In the meantime
provide debug messages.

Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Suggested-by: default avatarMatthew Wilcox <willy@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3565fce3

fs/dax.c

+57 −8
Original line number Diff line number Diff line
@@ -558,6 +558,24 @@ EXPORT_SYMBOL_GPL(dax_fault); 
 */

#define PG_PMD_COLOUR	((PMD_SIZE >> PAGE_SHIFT) - 1)



static void __dax_dbg(struct buffer_head *bh, unsigned long address,

		const char *reason, const char *fn)

{

	if (bh) {

		char bname[BDEVNAME_SIZE];

		bdevname(bh->b_bdev, bname);

		pr_debug("%s: %s addr: %lx dev %s state %lx start %lld "

			"length %zd fallback: %s\n", fn, current->comm,

			address, bname, bh->b_state, (u64)bh->b_blocknr,

			bh->b_size, reason);

	} else {

		pr_debug("%s: %s addr: %lx fallback: %s\n", fn,

			current->comm, address, reason);

	}

}



#define dax_pmd_dbg(bh, address, reason)	__dax_dbg(bh, address, reason, "dax_pmd")



int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,

		pmd_t *pmd, unsigned int flags, get_block_t get_block,

		dax_iodone_t complete_unwritten)
@@ -581,21 +599,29 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, 
	/* Fall back to PTEs if we're going to COW */

	if (write && !(vma->vm_flags & VM_SHARED)) {

		split_huge_pmd(vma, pmd, address);

		dax_pmd_dbg(NULL, address, "cow write");

		return VM_FAULT_FALLBACK;

	}

	/* If the PMD would extend outside the VMA */

	if (pmd_addr < vma->vm_start)

	if (pmd_addr < vma->vm_start) {

		dax_pmd_dbg(NULL, address, "vma start unaligned");

		return VM_FAULT_FALLBACK;

	if ((pmd_addr + PMD_SIZE) > vma->vm_end)

	}

	if ((pmd_addr + PMD_SIZE) > vma->vm_end) {

		dax_pmd_dbg(NULL, address, "vma end unaligned");

		return VM_FAULT_FALLBACK;

	}



	pgoff = linear_page_index(vma, pmd_addr);

	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;

	if (pgoff >= size)

		return VM_FAULT_SIGBUS;

	/* If the PMD would cover blocks out of the file */

	if ((pgoff | PG_PMD_COLOUR) >= size)

	if ((pgoff | PG_PMD_COLOUR) >= size) {

		dax_pmd_dbg(NULL, address,

				"offset + huge page size > file size");

		return VM_FAULT_FALLBACK;

	}



	memset(&bh, 0, sizeof(bh));

	block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
@@ -611,8 +637,10 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, 
	 * just fall back to PTEs.  Calling get_block 512 times in a loop

	 * would be silly.

	 */

	if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)

	if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) {

		dax_pmd_dbg(&bh, address, "allocated block too small");

		goto fallback;

	}



	/*

	 * If we allocated new storage, make sure no process has any
@@ -635,23 +663,33 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, 
		result = VM_FAULT_SIGBUS;

		goto out;

	}

	if ((pgoff | PG_PMD_COLOUR) >= size)

	if ((pgoff | PG_PMD_COLOUR) >= size) {

		dax_pmd_dbg(&bh, address, "pgoff unaligned");

		goto fallback;

	}



	if (!write && !buffer_mapped(&bh) && buffer_uptodate(&bh)) {

		spinlock_t *ptl;

		pmd_t entry;

		struct page *zero_page = get_huge_zero_page();



		if (unlikely(!zero_page))

		if (unlikely(!zero_page)) {

			dax_pmd_dbg(&bh, address, "no zero page");

			goto fallback;

		}



		ptl = pmd_lock(vma->vm_mm, pmd);

		if (!pmd_none(*pmd)) {

			spin_unlock(ptl);

			dax_pmd_dbg(&bh, address, "pmd already present");

			goto fallback;

		}



		dev_dbg(part_to_dev(bdev->bd_part),

				"%s: %s addr: %lx pfn: <zero> sect: %llx\n",

				__func__, current->comm, address,

				(unsigned long long) to_sector(&bh, inode));



		entry = mk_pmd(zero_page, vma->vm_page_prot);

		entry = pmd_mkhuge(entry);

		set_pmd_at(vma->vm_mm, pmd_addr, pmd, entry);
@@ -668,8 +706,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, 
			result = VM_FAULT_SIGBUS;

			goto out;

		}

		if (length < PMD_SIZE

				|| (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR)) {

		if (length < PMD_SIZE) {

			dax_pmd_dbg(&bh, address, "dax-length too small");

			dax_unmap_atomic(bdev, &dax);

			goto fallback;

		}

		if (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR) {

			dax_pmd_dbg(&bh, address, "pfn unaligned");

			dax_unmap_atomic(bdev, &dax);

			goto fallback;

		}
@@ -680,6 +723,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, 
		 */

		if (pfn_t_has_page(dax.pfn)) {

			dax_unmap_atomic(bdev, &dax);

			dax_pmd_dbg(&bh, address, "pfn not in memmap");

			goto fallback;

		}
@@ -692,6 +736,11 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, 
		}

		dax_unmap_atomic(bdev, &dax);



		dev_dbg(part_to_dev(bdev->bd_part),

				"%s: %s addr: %lx pfn: %lx sect: %llx\n",

				__func__, current->comm, address,

				pfn_t_to_pfn(dax.pfn),

				(unsigned long long) dax.sector);

		result |= vmf_insert_pfn_pmd(vma, address, pmd,

				dax.pfn, write);

	}